a) Field of the Invention
The present invention relates to a booster and method for boosting the output of a low-power burst transmitter and also to a burst transmission apparatus using such a booster.
b) Description of the Prior Art
When using a low-power transmitter, it is preferred to provide a booster on the output side of the transmitter. More particularly, a low-power transmitter having its output insufficient to provide the required output must be boosted up to that required output. If the low-power transmitter is of a continuous transmission type, its transmission output may be boosted according to such a principle as described in U.S. Ser. No. 07/455156 filed on Dec. 22, 1989 or Japanese Patent Laid-Open No. Hei 3-76430.
FIG. 6A shows a continuous transmission apparatus comprising a low-power transmitter 100 and a booster 200 connected to the later part of the transmitter. The low-power transmitter 100 comprises a power amplifier (PA) 110, an automatic power controller (APC) 120 and a control circuit 130. The booster 200 comprises a PA 210 and an APC 220.
The PA 110 of the low-power transmitter 100 receives a transmission signal through a transmission signal input terminal 100a and then power-amplifies the transmission signal. The amplified transmission signal is outputted from an antenna connection terminal 140. If the use of the booster 200 is not required, that is, if the output transmission level of the low-power transmitter 100 satisfies the required level, the antenna connection terminal 140 is connected to an antenna to transmit the output of the PA 110 out of the antenna. However, if there is a possibility potential of not satisfy the required transmission output level in the low-power transmitter 100, the antenna connection terminal 140 is then connected to a transmission signal input terminal 250 of the booster 200 as shown. In such a connection, a transmission signal outputted from the antenna connection terminal 140 is received by the PA 210 of the booster 200 through the transmission signal input terminal 250. The PA 210 then power-amplifies this transmission signal. The amplified transmission signal is fed from an antenna connection terminal 270 to an antenna (not shown).
The power amplification of the PA 110 or 210 is controlled directly by the APC 120 or 220. More particularly, each of the APC 120 or 220 is adapted to sense the output power level of the corresponding PA 110 or 210 to feedback control the amplification factor of the PA 110 or 210 on the sensed level. Thus, the output power level of the PA 110 or 210 can be controlled into a target level. The target level is provided by the control circuit 130.
The control circuit 130 receives and responds to a command relating to the necessary power level from a base station (not shown) to provide the target value to the respective one of the APCs 120 and 220. These target values are allocated to the APCs 120 and 220 so that the output power level of the PA 210 will be the power level commanded by the base station. Reference numerals 150 and 260 in FIG. 6A denote control signal output and input terminals, respectively. When the booster 200 is used, the control signal output and input terminals are connected to each other. When the booster 200 is not used, the control signal output and input terminals are disconnected from each other and the control circuit 130 provides a target value to the APC 120 such that the power level commanded by the base station can be realized only by the PA 110.
In such a prior art system, therefore, the output power levels of the PAs 110 and 210 are continuously and constantly controlled by the APCs 120 and 220. Since the target values relating to such a control are suitably given depending on the commanded power level from the control circuit 130, the output of the low-power transmitter 100 can be boosted up to the commanded power level.
However, the boost based on such a principle can be applied only to the continuous transmission type low-power transmitter 100, but not to a burst transmission. The continuous transmission is that signals are continuously sent out time, as shown in FIG. 7A. The burst transmission is that a station can send out signals only within a time slot assigned to itself, as shown in FIG. 7B. The burst transmission is executed by a TDMA (Time Division Multiple Access) communication system.
The reasons why the boost principle shown in FIGS. 6A and 6B cannot be applied to the burst transmission are that the output power level of the
210 is continuously and constantly controlled and also that the burst transmission permits transmission signals to be outputted only within a time slot assigned to each of local stations.
It is now assumed that the boost principle shown in FIGS. 6A and 6B is applied to the burst transmission. Namely, assume that transmission signals inputted into the booster 200 are burst signals for carrying data only within a time slot assigned to the respective one of local stations. What is inherently required by the burst transmission is the output of transmission signals only within an assigned time slot. When the output power level of the PA 210 as shown in FIGS. 6A and 6B is continuously and constantly controlled, however, transmission signals will unintentionally be outputted within a time slot not assigned to that station. This means that the boost principle shown in FIGS. 6A and 6B cannot be applied to the burst transmission.